Artificial receptors that are capable of selectively binding anionic species show promise in the diagnosis and treatment of diseases and in environmental remediation (Beer, P. D.; Gale, P. A. Angew. Chem. Int. Ed. 2001, 40, 486; Gale, P. A. Coord. Chem. Rev. 2000, 199, 181; Snowden, T. S.; Anslyn, E. V. Curr. Opin. Chem. Biol. 1999, 3, 740; Antonisse, M. M. G.; Reinhoudt, D. N. Chem. Commun. 1998, 443; Beer, P. D. Acc. Chem. Res. 1998, 31, 71; Schmidtchen, F. P.; Berger, M. Chem. Rev. 1997, 97, 1609). For example, sensors for inorganic phosphate could be used to monitor ATP synthesis/hydrolysis or kinase-dependent cell signaling. “Carrier” molecules can also enhance through-membrane transport of chloride ion, which is a goal of cystic fibrosis research. Anion binding species may also be used in the extraction of nitrate from rivers and lakes, which is expected to inhibit eutrophication, and the associated oxygen depletion and fish kills. In addition, extraction of anions from nuclear waste prior to vitrification may decrease nuclear waste volume.
Several anion receptors have been constructed from 5-membered heterocycles (Sessler, J. L.; Davis, J. M. Acc. Chem. Res. 2001, 34, 989; Cafeo, G.; Kohnke, F. H.; La Torre, G. L.; White, A. J. P.; Williams, D. J. Chem. Commun. 2000, 1207; Anzenbacher, P., Jr.; Jursíková, K.; Sessler, J. L. J. Am. Chem. Soc. 2000, 122, 9350; Miyaji, H.; Sato, W.; Sessler, J. L. Angew. Chem. Int. Ed. 2000, 39, 1777; Sessler, J. L.; Allen, W. E. CHEMTECH 1999, 29, 16; Sato, K.; Arai, S.; Yamagishi, T. Tetrahedron Lett. 1999, 40, 5219), (thio)amides (Ayling, A. J.; Pérez-Payán, M. N.; Davis, A. P. J. Am. Chem. Soc. 2001, 123, 12716; Choi, K.; Hamilton, A. D. J. Am. Chem. Soc. 2001, 123, 2456; Miyaji, H.; Sessler, J. L. Angew. Chem. Int. Ed. 2001, 40, 154; Jagessar, R. C.; Burns, D. H. Chem. Commun. 1997, 1685), or both (Gale, P. A.; Camiolo, S.; Tizzard, G. J.; Chapman, C. P.; Light, M. E.; Coles, S. J.; Hursthouse, M. B. J. Org. Chem. 2001, 66, 7849), because these groups form relatively strong NH-anion hydrogen bonds. Previous work has also established that coupling luminescent moieties to H-bond donors can yield sensors that operate at low anion concentrations (Liao, J.-H.; Chen, C.-T.; Fang, J.-M. Org. Lett. 2002, 4, 561; Gunnlaugsson, T.; Davis, A. P.; Glynn, M. Chem. Commun. 2001, 2556; Sun, S.-S.; Lees, A. J. Chem. Commun. 2000, 1687; Beer, P. D.; Szemes, F.; Balzani, V.; Salà, C. M.; Drew, M. G. B.; Dent, S. W.; Maestri, M. J. Am. Chem. Soc. 1997, 119, 11864). We describe here a series of anion receptors that incorporate all of these features into a single molecular unit (Sessler, J. L.; Maeda, H.; Mizuno, T.; Lynch, V. M.; Furuta, H. Chem. Commun. 2002, 862; Anzenbacher, P., Jr.; Try, A. C.; Miyaji, H.; Jursiková, K.; Lynch, V. M.; Marquez, M.; Sessler, J. L. J. Am. Chem. Soc. 2000, 122, 10268; Black, C. B.; Andrioletti, B.; Try, A. C.; Ruiperez, C.; Sessler, J. L. J. Am. Chem. Soc. 1999, 121, 10438). Specifically, electrically neutral biimidazole diamides are shown to simultaneously serve as multiple H-bond donors (Fortin, S.; Beauchamp, A. L. Inorg. Chem. 2000, 39, 4886) and as anion-sensitive fluorophores.